Art of casting pistons



Dec. 7, 1937. BLETTNER 2,101,046

ART OF CASTING PISTONS Filed July 1, 1957 2 Sheets-Sheet 1 Dec. 7, 1937. BLETTNE'R 2,101,046

ART OF CASTING PISTONS Filed July 1, 1937 2 Sheets-Sheet 2 5 $517753 faoye 7/ 19%6flfiif Patented Dec. 7, 1937 UNITED STATES ART OF CASTING PISTONS George H. Blettner, Chicago, Ill., assignor .to Renette Company, Chicago, 111., a corporation of Illinois Application July 1, 1937, Serial No. 151,335

3 Claims.

The present invention relates to the art of 'casting pistons, and has to do with a novel method of casting pistons for internal combustion engines and like uses.

An object of the present invention is to provide a method of casting pistons for internal combustion engines in multiple, in such manner that shrink cracks and porosity are materially reduced.

1 Another object of the invention has to do with a novel method of casting pistons, in multiple or in groups, whereby foundry losses are reduced and the manufacturing costs per piston materially reduced for quantity production.

A further object of the present invention is to provide a novel method of casting pistons, in groups or in multiple, wherein a plurality of piston casting cavities are served by a single feeder and by which molten metal is directed. and supplied to the piston casting cavities in such manner as to retard the rate of cooling of the sections constituting the closed head ends of the piston castings by freely interchanging heat and metal between the supply passages and the castings to' compensate for shrinkage of the piston castings while cooling. I

The above, other and further objects of the present invention will be apparent from the following description and accompanying drawings. The. accompanying drawings illustrate one form of mold of assembled sections, in connection with which the process of the present invention may be practiced, and also illustrate castings made in accordance with the principles of the present invention, and the views thereof are as follows:

Figure 1 is an isometric view of a piston casting mold of assembled sections, fashioned to form four piston castings per pouring.

Figure 2 is a top plan view of a resultant casting made from the mold of Figure 1, showing the feeder in section and illustrating the preferred connections to the castings from the feeder.

Figure 3 is a side elevational view of a group of four pistons cast in a sectional mold in accordance with the principles of the present invention, and showing a single feeder and plural connections to the castings, and in dottedlines, reductions in sizes of the feeder, occasioned by 6 the withdrawal of materialto the piston castings while cooling to compensate for shrinkage.

Figure 4 is an end elevational view of the arrangement of Figure 3.

Figure 5 is a view through one section; of the 5 mold showing certain parts in plan and certain parts in section, and illustrating the relationship between the feeder, the piston castings and the connections from the feeder to the casting cavities, with the cores in position for forming the openings in the wrist pin bosses of the pistons. 5 The sectional portion of this figure is taken substantially in the plane indicated by the "line V--V of Figure 6. Figure 6 is a vertical sectional view through the mold and casting of Figure 5. 10 Figure '7 is a plan view, with a part in section, a of a group casting, showing four pistons per'tier and the connections to the pistons from the feeder. v

The drawings will now be explained. 15 For the purpose of explanation and illustration,

the mold sections have been shown as formed of sand by use of a follow board. The mold illustrated in Figure 1 includes four sections l, 2, 3 and. 4, which are assembled ready for the casting of four pistons. The top section is provided with an enlarged opening 5 to the feeder 6.

Referring to Figures 2 and 3, it will be observed that the pistons in each tier are connected by a pair of shrinkage members I l, the center lines of which preferably lie in the plane of the axes of the pistons in the tier and on eachside of said axes.

Extending from the 'common feeder 6 to the shrinkage members II are runners l2 which are 30 parallel to, and adjacent the heads of the cavities. The feeder 6, runners l2 and shrinkage members II are in compact arrangement so that when the cavities are filled with metal the heat in the feeder and the connections between it 35 and the cavities will tend to retard the rate of cooling of the head end portions ofthe pistons. Y

In casting, metal is poured into the feeder 6 which is in vertical position. The metal flows 4o downwardly through the feeder, laterally through the runners l2 into the shrinkage members II and thence into the cavities, all of the cavities being filled substantially simultaneously, thereby supplying metal equally to all of the cavities.

In Figure 7, the shrinkage members I! connect the several pistons B in a tier, and runners l2 extend from the common feeder 6 to the shrinkage members.

In this form of theinvention, the metal in the feeder and the connections to the several cavities provides a supply of metal adjacent the heavier sections of the pistons, such as to maintain some of the metal in the connections sufliciently fluid to be available to the casting to compensate for ing cavities 8, arranged with the head forming portions of the cavities in opposed relation and both closely adjacent the feeder 6, which feeder is formed in the mold by a suitable pattern on the follow board. Also on the follow board are connections from the feeder 6 to the piston casting cavities, which constitute the runners l2 and the shrinkage members II. The connec- I tions from the common feeder 6 to the cavities are of such nature as to supply molten metal to the larger voids in the cavities when the mold is in casting position, and also to retard the rate of cooling of the closed end sections of the pistons as well as to' freely interchange heat and metal to compensate for shrinkage of the castings while cooling.

After one of the sections of the mold has been made as described, its companion section is made and positioned after the cores are set. I Thus two sections are fashioned to form two complete pistons; thereafter, additional sections or units are made and assembled to form as many tiers of pistons as may be desired to be cast from the single or common feeder 6.

After two mating sections or units of the mold havebeen formed, the cores 9 are inserted, and

- the cores I0 for the wrist pinopenings are spaced in the cores, and then another pair of sections put on top of the first pair, and the process continued until the requisite number of pairs of sec tions or units has been reached. When assembled, the single feeder 6 is ready for supply of molten metal to all of the piston casting cavities formed in the mold.

The core prints utilized for providing recesses I for the wrist pin cores I!) serve to tie in the cores 9 when the same are inserted in the cavities 8. At the time the cores 9 are made, provision is made for forming vents l3. This may be accomplished by perforations made to carry the expelled gases to such parts of the mold as not to interfere With any of the piston casting cavities being filled with metal during the pouring operation.

In carrying out the process of the present invention, molten metal is poured through the feeder 6, filling all the cavity spaces in the mold as Well as the runners and shrinkage members. When the metal has been poured, so as to fill the common feeder 6 up to near its top, that is, adjacent the opening 5, pouring ceases.

Because of the manner of connecting the piston forming cavities to the single or common feeder 6, and because of the close proximity of the head forming ends of the cavities to the feeder and connections, and because the supply connections to the piston forming cavities communicate therewith adjacent the larger voids of the cavities, introduction of molten metal into the cavities, connections and feeder, serves to retard the rate of cooling of the piston sections forming the closed head ends of the castings,,and also serves to maintain the metal sufiiciently fluid to compensate for shrinkage of the piston castings without restriction while cooling, thus assuring fully formed and complete castings, free from cracks 'to properly form the mold cavities.

When the casting has cooled sufficiently, the sand is broken away, leaving a rough casting,

such as that shown in Figures 2, 3 and 4. The

pistons represented in A are then severed from the connections, and the sprue is melted for further casting operations.

It will be observed that the connections to the cavities at the larger voids from the feeder are so constructed that in forming .the castings, molten, metal is flowed across and in close proximity to the head forming ends of the cavities, to conserve heat and retard the rate of cooling of the closed head ends of the piston castings. By forming the castings with the axes of the wrist pin bosses horizontal, when the mold is in casting position, full and complete formation of the heavier sections of the castings is secured, as the metal in the feeder and connections is maintained sufficiently fluid for long enough time to readily give or take additional metal to or from the heavier sections of the castings, while the latter are cooling.

In casting aluminum or steel pistons, a breathing action takes place between the metal in the castings and the metal in the connections and feeder, during cooling of the castings. Such breathing action results in drawing of metal from the feeder and connections-into the heavier sections of the castings to compensate for shrinkage of the castings, and inversely, by retarding the cooling of the, closed head end sections of the castings, and assures uniform castings as to texture and that all of the parts and sections of the various pistons are completely fashioned without shrink cracks, porosity or other imperfections.

In carrying out the process of the present invention, as practiced with the sectional mold, it has been found convenient to arrange the piston casting cavities in tiers which are vertically spaced when the mold is in casting position. The casting illustrated in Figures 2 and 3 was made with two pistons per tier. It is, of course, to be understood that two or more pistons per tier might be cast, following the teachings of the present invention, or that but a single piston per tier might be formed.

The size and degree of proximity of the central feeder, the castings, and the connections from the feeders to the cavities, with the channels crossing the spans of the closed head ends of the cavities, definitely control the rate of cooling of the head end portions of the piston cavities, and may be varied in accordance with their proportions, size and materials.

. The manner in which the supply of molten metal is directed to the cavities enables free interchange of metal between the supply and the castings within the cavities which continue to give and take metal over the period of time required for the cooling ofthe castings.

The arrangement of pistons per tier and the number of castings to be fashioned per pouring may be subject to the advice of the designer or engineer, in order that a completeset of pistons per pouring may be made.

By making the mold in sections or units, it is possible to reduce the amount of sand necessary When the mold is in casting position, the several sections are shallow enough to require but slightly more than the amount of sand necessary to form the mold cavities, thus reducing the cost of molding and lightening the labor of the mold maker, as he does not have to handle as much sand. By having the mold in sections, with the various cavities and connections as close together as good foundry practice demands, the amount of sprue per pouring is reduced to a minimum.

The cores 9 are formed of sand and are mounted on studs l2, so that when the cores are inserted in the mold sections, as illustrated in Figure 1, the skirt ends of the piston forming cavities will be closed, and the cores will be in position to form the interiors of the piston castings. Preferably, in inserting the cores, the portions thereof which form the wrist pin bosses of the castings are disposed so that the axes of the wrist pin boss forming portions are horizontal when the mold is in casting position. p

The invention is claimed as follows: 1. That improvementin the method of simultaneously casting a plurality of internal combustion engine pistons, which comprises thesteps of forming in a mold a plurality of piston casting cavities in tier formation with their axes horizontal and with the head forming ends of the cavities in each tier facing each other, forming in the mold a single feeder which is vertical when the mold is in casting position and which extends downwardly in closely adjacent relation between and past the head ends of the cavities in the tiers, forming in the mold connections from the feeder to each cavity and pouring metal into said feeder to supply metal to the cavities on each side of the axis of each cavity in such manner that the heat of the metal in the feeder and connections tends to retard the rate of cooling of the head end portions of the piston castings.

2. That improvement in the method of simultaneouslycasting a plurality of internal combustion engine pistons, which comprises the steps of forming in a mold a plurality of piston casting cavities in tier formation with their ,axes horizontal and with the head forming ends of the cavities in each tier facing each other, forming in the mold a single feeder which is vertical -when the mold is in casting position and which extends downwardly in closely adjacent relation between and past the head ends of the cavities in the. tiers, forming in the molds two connections from the feeder to each cavity arranged to communicate with each cavity on each side of the .axis thereof and in horizontal zones at substanp tially mid-height of each cavity, and pouring metal into said feeder for distribution through said connections'into said cavities.

3. That improvement in the art of simultaneously forming a plurality of internal combustion engine pistons; which comprises forming in a mold a plurality of piston cavities arrangedin tiers with two cavities to a tier and with the axes horizontal and with the head forming ends of the cavities in each tier fa'cingeach other, forming in the mold a single feeder which is vertical when the mold is in casting position and which extends downwardly between and past and in close proximity to the facing head ends of the cavities in the several tiers, and supplying metal to the cavities from the feeder in paths parts of which extend along the lengths of the cavities on both sidesof the horizontal axes thereof at subs'tantially mid-height and parts of which paths extend entirely across and in close proximity to the head forming ends of the cavities in such manner that the heat of the metal in the feeder and paths retards the rate of cooling of the closed head end portions of the piston castings.

GEORGE H. BLET'I'NER. 

